1. Technical Field
The present disclosure relates generally to a bridgeless power factor corrector and a method of operating the same, and more particularly to a bridgeless power factor with a single choke and a method of operating the same.
2. Description of Related Art
PFC (power factor correction) circuit is widely used as a power conversion circuit in electronic devices at present. The PFC circuit is provided to correct the power factor of the AC power source to bring it as close to unity. The PFC can be expressed utilization efficiency of the electrical power for the electronic products: higher power factor, higher utilization efficiency of the electrical power, and vice versa. Accordingly, electronic products usually provide a PFC function to significantly increase utilization efficiency of the electrical power.
Reference is made to FIG. 1 which is a circuit diagram of a related art full-bridge power factor corrector. Because the boost power factor corrector (boost PFC) can achieve effects of higher power factor and lower harmonic, the boost PFC is usually provided for power factor correction. The boost PFC is composed of a bridge rectifier 12A, a choke 13A, a switch 14A, a diode 15A, a resistor 16A, and a capacitor 17A. The boost PFC is electrically connected to an external AC power source 10A and a PFC controller (not shown) is provided to control the switch 14A according to the input current and input voltage of the external AC power source 10A so that phase of the input current follows phase of the input voltage to achieve high power factor by switching the switch 14A using a high-frequency scheme. In addition, an EMI filter 11A can be also installed between the external AC power source 10A and the boost PFC to eliminate noise in the external AC power source 10A.
For the traditional boost PFC, however, a plurality of bridge diodes of the bridge rectifier 12A produce a higher proportion of power losses comparing with the whole conversion losses, thus reducing the conversion efficiency.
Reference is made to FIG. 2 which is a circuit diagram of a related art bridgeless power factor corrector. The bridgeless power factor corrector (bridgeless PFC) includes a first choke 23_1A, a second choke 23_2A, a first switch 24_1A, a second switch 24_2A, a first diode 25_1A, a second diode 25_2A, a resistor 26A, a capacitor 27A, a first rectify diode 28_1A, a second rectify diode 28_2A, a first bypass diode 29_1A, and a second bypass diode 29_2A. The bridgeless PFC is electrically connected to an external AC power source 20A and a PFC controller (not shown) is provided to control the first switch 24_1A and the second switch 24_2A according to the input current and input voltage of the external AC power source 20A so that phase of the input current follows phase of the input voltage to achieve high power factor by switching the first switch 24_1A and the second switch 24_2A using a high-frequency scheme. In addition, an EMI filter 21A can be also installed between the external AC power source 20A and the bridgeless PFC to eliminate noise in the external AC power source 20A.
The traditional bridgeless PFC uses two chokes (namely, the first choke 23_1A and the second choke 23_2A) for storing energy and releasing energy. Also, one choke works when the external AC power source 20A is in a positive half cycle and the other choke works in a negative half cycle that is one of the two chokes is in an idle condition whether the external AC power source 20A is in the positive half cycle or the negative half cycle. Therefore, utilization rate of the two chokes is lower. In addition, the required occupied space of the two chokes is usually larger due to inherent characteristics of the choke, such as the core, the winding thereof.
Accordingly, it is desirable to provide a bridgeless power factor corrector with a single choke to correct the power factor of the AC power source, increase conversion efficiency, and reduce occupied space and increase utilization rate of the choke element.